T1-weighted turbo-spin-echo mri sequence for producing high quality dark blood images at high heart rates

ABSTRACT

A T1-weighted turbo-spin-echo magnetic resonance imaging system configured to capture data associated with a subject&#39;s heart during a time period and produce MR images has a dark-blood preparation module, a data capture module, and an image reconstruction module. The dark-blood preparation module performs dark-blood preparation through double inversion during some, but not all of the heartbeats within the time period. The data capture module configured performs data readouts to capture imaging data of an imaging slice during every heartbeat in which dark-blood preparation is performed. The data capture module also performs a steady state maintenance step during every heartbeat in which dark-blood preparation is not performed in order to maintain maximum T1-weighting. The image reconstruction module configured to reconstruct a T1-weighted image based on the imaging data.

TECHNICAL FIELD

The present invention relates generally to cardiovascular MagneticResonance Imaging (MRI), and, more particularly, to T1-weightedturbo-spin echo (TSE) imaging in a sequence which produces high qualitydark blood images at high heart rates.

BACKGROUND

The dark-blood T1-weighted turbo-spin echo (TSE) sequence is a standardMRI pulse sequence that is commonly used for depicting cardiac andvascular morphology and for diagnosing cardiac tumors. In dark-bloodimaging, pulses are timed to capture a null signal from flowing bloodand thus represent the blood as a dark area in the image. Dark bloodtechniques are especially useful for visualizing intracavitary cardiacmasses, which appear brighter than the dark blood pool in the cavity.The MRI pulse sequence is synchronized to a physiological signal such asan electrocardiogram (ECG) or a pulse oximetry signal, and a portion ofthe image is read out (acquired) at each heartbeat by each echo train.In T1-weighted TSE (as opposed to T2-weighted TSE) the sequence isalways arranged to readout at every heart beat (trigger pulse=1)resulting in the shortest possible effective time-to-repeat (TR)(equaling one RR-interval) to provide maximum T1-weighting.

Blood appears dark if its magnetization is zero at the time of the TSEdata readout. Blood of non-zero magnetization is erroneously spatiallyencoded due to the flow- and motion-sensitivity of the TSE readout andcan appear smeared across the entire image as a bright “haze.” As aresult, myocardium cannot be seen or its signal intensity is erroneouslyaltered to disguise or misrepresent myocardial abnormalities.Intracavitary cardiac tumors can be missed due to this haze or due tothe equal image intensity of a tumor and non-darkened blood.

Using conventional methods, TSE images depict blood sufficiently dark insubjects with low heart rates such that the contrast between blood andtissue is clear and the images can be relied upon for a diagnosis.Unfortunately, the capability of the dark-blood preparation to renderblood magnetization zero is diminished with increasing heart rates,which are often found in cardiac subjects and naturally occur inchildren. In these subject groups, dark-blood performance of thestandard T1-weighted TSE sequence is frequently so poor that imagequality is insufficient to rely on for a diagnosis. Dark-bloodperformance is poor at higher heart rates using a T1-weighted TSEsequence because with the pulses occurring at every heartbeat, DB-prepoccurs too often and blood magnetization recovers too quickly for thedata capture to coincide with both the zero magnetization point and theheart being in diastole.

Dark-blood performance could be improved if the pulse sequence wassynchronized not to every heartbeat, but to every other or every thirdheartbeat (trigger pulse=2 or 3). This would allow for a longereffective TR of two or three RR-intervals. Blood magnetization wouldthen be about zero at the diastolic TSE readout in the dark-bloodprepared heartbeats and would thus appear dark in the image, therebyavoiding artifacts. In other words, allowing for more time betweendark-blood preparations allows the data readout to be timed to thezero-magnetization point of the blood. However, T1-weighted TSE cannotbe adequately run with a trigger pulse of 2 or 3. Therefore, analternative approach for improving dark-blood performance in T1-weightedTSE imaging at high heart rates is needed.

The present disclosure is directed to overcoming these and otherproblems of the prior art.

SUMMARY

Embodiments of the present invention address and overcome one or more ofthe above shortcomings and drawbacks, by providing methods, systems, andapparatuses related to a T1-weighted turbo-spin-echo MRI sequence thatproduces high quality dark blood images at high heart rates.

In an exemplary embodiment, a computer-implemented method for performinga cardiovascular T1-weighted turbo-spin-echo magnetic resonance imagingsequence includes receiving a physiological signal from a subject, thephysiological signal representative of the subject's heartbeat, andperforming dark-blood preparation according to a trigger pulse of N,wherein the dark-blood preparation occurs only in every Nth heartbeatand N is greater than 1. The method also includes performing a datareadout in every Nth heartbeat, wherein the data readout includescapturing imaging data associated with an imaging slice, and performinga steady-state maintenance step, wherein the steady-state maintenancesteps are performed only for every heartbeat which does not include adata readout. The method further includes reconstructing a T1-weightedimage of the imaging slice based on the imaging data received as aresult of the data readouts.

In another exemplary embodiment, a computer-implemented method forproducing a cardiovascular T1-weighted magnetic resonance image includesreceiving a parameter representative of a subject's heartrate,determining a trigger pulse value N for an MRI sequence based on theparameter representative of the subject's heartrate, and performing theMRI sequence. The MRI sequence includes performing dark-bloodpreparation according to a trigger pulse of N, wherein the dark-bloodpreparation occurs only in every Nth heartbeat, and performing one of adata readout or a steady-state maintenance step for every heartbeat,wherein the data readout includes capturing imaging data associated withan imaging slice and both the data readout and the steady-statemaintenance step saturate transverse and longitudinal magnetization ofthe tissue. The method further includes reconstructing a T1-weightedimage of the imaging slice based on the imaging data received as aresult of the data readouts.

In another exemplary embodiment, a T1-weighted turbo-spin-echo magneticresonance imaging system configured to capture data associated with asubject's heart during a time period and produce MR images includes adark-blood preparation module, a data capture module, and an imagereconstruction module. The dark-blood preparation module is configuredto perform dark-blood preparation through double inversion during some,but not all of the heartbeats within the time period. The data capturemodule is configured to perform data readouts to capture imaging data ofan imaging slice during every heartbeat within the time period. Theimage reconstruction module is configured to reconstruct a T1-weightedimage based on the imaging data. The image reconstruction modulediscards or ignores imaging data received from the data capture modulewhich was captured during heartbeats in which the dark-blood preparationmodule did not perform dark-blood preparation.

Additional features and advantages of the invention will be madeapparent from the following detailed description of illustrativeembodiments that proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of the present invention are bestunderstood from the following detailed description when read inconnection with the accompanying drawings. For the purpose ofillustrating the invention, there are shown in the drawings embodimentsthat are presently preferred, it being understood, however, that theinvention is not limited to the specific instrumentalities disclosed.Included in the drawings are the following Figures:

FIG. 1A is a schematic diagram of an exemplary MRI system, consistentwith disclosed embodiments;

FIG. 1B is a schematic diagram of an exemplary control system for theMRI system of FIG. 1A, consistent with disclosed embodiments;

FIG. 2 is a diagram which illustrates some of the aspects of dark-bloodpreparation in cardiovascular MR imaging, specifically the optimaltiming between dark-blood preparation at the R-wave and the data readoutduring diastole;

FIG. 3 is a diagram which graphically represents a conventionaldark-blood prepared T1-weighted TSE MRI sequence with a low subjectheart rate, and the resulting blood magnetization which crosses thezero-line at the beginning of the data readout;

FIG. 4 is a diagram which graphically represents a conventionaldark-blood prepared T1-weighted TSE MRI sequence with a high subjectheart rate, and the resulting blood magnetization which is not zero atthe beginning of the data readout;

FIG. 5A is an MR image for a first slice location according to theconventional dark-blood prepared T1-weighted TSE MRI sequence with highsubject heart rate;

FIG. 5B is an MR image for a second slice location according to theconventional dark-blood prepared T1-weighted TSE MRI sequence with highsubject heart rate;

FIG. 6 is a flowchart of an exemplary dark-blood prepared T1-weightedTSE MRI sequence, consistent with disclosed embodiments;

FIG. 7 is a diagram which graphically represents an exemplary dark-bloodprepared T1-weighted TSE MRI sequence having a DB-prep trigger pulse ofgreater than one, consistent with disclosed embodiments;

FIG. 8 is a diagram which graphically represents another exemplarydark-blood prepared T1-weighted MRI sequence having a DB-prep triggerpulse of greater than one wherein slice-selective saturations areperformed;

FIG. 9 is a diagram which graphically represents yet another exemplarydark-blood prepared T1-weighted MRI sequence having a DB-prep triggerpulse of greater than one wherein a slice-selective saturation isperformed in the DB-module;

FIG. 10A is an MR image produced for a first slice location according toa disclosed T1-weighted MRI sequence having a DB-prep trigger pulse ofgreater than one with high subject heart rate;

FIG. 10B is an MR image produced for a second slice location accordingto a disclosed T1-weighted MRI sequence having a DB-prep trigger pulseof greater than one with high subject heart rate; and

FIG. 11 illustrates an exemplary computing environment within whichembodiments of the invention may be implemented.

DETAILED DESCRIPTION

The present disclosure describes a sequence for T1-weighted TSE MRIwhich accounts for heart rate. According to various embodiments of thepresent invention, as described in further detail herein, the MRIsequence utilizes an effective time-to-repeat (effective TR) needed foroptimal dark-blood performance, while still executing each TSE readoutat a trigger pulse of one. In some embodiments, a system identifies atrigger pulse which would place the data readout timing during anoverlap of the null point of blood after dark-blood preparation and theheart being in diastole. This value depends on the heart rate of thesubject at the time of imaging. The system then performs dark-bloodpreparation at the selected trigger pulse. During each heartbeat thatcontains such dark-blood preparation, a TSE readout is run to collect aportion of the data of one entire image. In the heartbeats withoutdark-blood preparation, a TSE readout is also run, but withoutcollecting data which will be subsequently used in reconstructing theimage. This TSE readout is a “dummy” readout which maintains the tissuemagnetization in a steady state of maximum or near-maximum T1-weighting.In this way, the T1-weighting of the tissue is not affected by thehigher trigger pulse. The resulting dark-blood performance issignificantly improved over a conventional T1-weighted sequence using atrigger pulse of one at higher heart rates, producing high qualityimages which can be relied upon for subject diagnosis.

FIG. 1A shows an MRI system 100 for ordering acquisition of frequencydomain components representing MRI data for storage in a k-space storagearray, as used by some embodiments of the present invention. In system100, magnetic coils 12 create a static base magnetic field in the bodyof patient 11 to be imaged and positioned on a table. Within the magnetsystem are gradient coils 14 for producing position dependent magneticfield gradients superimposed on the static magnetic field. Gradientcoils 14, in response to gradient signals supplied thereto by a gradientand shim coil control module 16, produce position dependent and shimmedmagnetic field gradients in three orthogonal directions and generatemagnetic field gradient pulses for magnetic resonance imaging pulsesequences. The shimmed gradients compensate for inhomogeneity andvariability in an MRI device magnetic field resulting from patientanatomical variation and other sources. The magnetic field gradientsinclude, for example, a dark-blood preparation magnetic field, aslice-selection gradient magnetic field, a phase-encoding gradientmagnetic field, and a data readout gradient magnetic field that areapplied to a selected anatomical area of interest of the patient 11.

A radio frequency (RF) module 20 provides RF pulse signals to RF coil18, which in response produces magnetic field pulses which rotate thespins of the protons in the imaged body of the patient 11 by 90 degreesor by 180 degrees for so-called “spin echo” imaging, or by angles lessthan or equal to 90 degrees for so-called “gradient echo” imaging.Gradient and shim coil control module 16 in conjunction with RF module20, as directed by central control system 26, control dark-bloodpreparation, data readout, slice-selection, phase-encoding, readoutgradient magnetic fields, radio frequency transmission, and magneticresonance signal detection, to acquire magnetic resonance signalsrepresenting planar slices of patient 11.

In response to applied RF pulse signals, the RF coil 18 receivesmagnetic resonance signals, i.e., signals from the excited protonswithin the body as they return to an equilibrium position established bythe static and gradient magnetic fields. The magnetic resonance signalsare detected and processed by a detector within RF module 20 and k-spaceordering processor unit 34 to provide a magnetic resonance dataset to animage data processor for processing into an image. In some embodiments,the image data processor is located in central control system 26.However, in other embodiments such as the one depicted in FIG. 1, theimage data processor is located in a separate unit 27. Electrocardiogram(ECG) signal processing 30 provides ECG signals used for pulse sequenceand imaging synchronization. A two or three dimensional k-space storagearray of individual data elements in k-space ordering processor unit 34stores corresponding individual frequency components comprising amagnetic resonance dataset. The k-space array of individual dataelements has a designated center and individual data elementsindividually have a radius to the designated center.

A magnetic field generator (comprising coils 12, 14, and 18) generates amagnetic field and a sequence of gradient (coils 14) and RF (coil 18)pulses for use in acquiring multiple individual frequency componentscorresponding to individual data elements in the storage array. Theindividual frequency components are successively acquired, for example,using an imaging trajectory with a radial path as described in furtherdetail below. A storage processor in the k-space ordering processor unit34 stores individual frequency components acquired using the magneticfield in corresponding individual data elements in the array. The radiusof respective corresponding individual data elements alternatelyincreases and decreases as multiple sequential individual frequencycomponents are acquired. The magnetic field acquires individualfrequency components in an order corresponding to a sequence ofsubstantially adjacent individual data elements in the array andmagnetic field gradient change between successively acquired frequencycomponents which is substantially minimized.

Central control system 26 uses information stored in an internaldatabase to process the detected magnetic resonance signals in acoordinated manner to generate high quality images of a selectedslice(s) of the body (e.g., using the image data processor) and adjustsother parameters of system 100. The stored information comprisespredetermined pulse sequence and magnetic field gradient and strengthdata as well as data indicating timing, orientation and spatial volumeof gradient magnetic fields to be applied in imaging. Generated imagesare presented on display 40 of the operator interface. Computer 28 ofthe operator interface includes a graphical user interface (GUI)enabling user interaction with central control system 26 and enablesuser modification of magnetic resonance imaging signals in substantiallyreal time. Continuing with reference to FIG. 1A, display processor 37processes the magnetic resonance signals to reconstruct one or moreimages for presentation on display 40, for example. Various techniquesknown in the art may be used for reconstruction.

FIG. 1B is a schematic illustration of a plurality of modules which areprovided in the MRI system 100. In the embodiment, of FIG. 1B, thesemodules are provided at the control system 26. However, it should beunderstood that these modules, which may be implemented in hardwareand/or software, may be provided anywhere in MRI system 100. Moreover,each module may be configured to communicate with a particular componentof the MRI system 100 in order to carry out a function, such as DB-prep,data readout, or image reconstruction. In an exemplary embodiment, theplurality of modules include a magnetic preparation module commonlyknown as a dark-blood preparation module (DB-prep module) 110, a datacapture module 120, and an image reconstruction module 130. In order toproduce images with dark-blood, the DB-prep module 110 is configured tosend magnetization signals to prepare an area of a heart to be imaged.The data capture module 120 thereafter performs a data readout tocapture data of a selected slice of the prepared area-based in part onthe magnetization of the features (e.g., tissue, blood, etc.). TheDB-prep module 110 sending signals and the data capture module 120performing a data readout are paired steps which result in a snapshot ofrelevant data at a particular time. These paired steps are repeatedseveral times to capture more and more data for the image. The imagereconstruction module 130 translates the resulting data from differentinstances into an image of the heart in a manner known in the art.

In part to ensure that captured data includes the heart in the same orsimilar position at each data point, the paired steps are timedaccording to the cycles of the heart. The time needed by the heart toperform one full cardiac cycle is referred to as an “RR-interval” as itfalls between two consecutive R-waves (peaks of an ECG wave). It is tobe understood that the terms “cardiac cycle,” “cycle,” “heartbeat,” and“RR-interval” are used interchangeably within the scope of thisdisclosure.

There are a number of parameters which must be set for MRI system 100 toperform an imaging sequence. These parameters include time-to-echo (TE),number of echoes per echo-train (also called turbo-factor (TF) orecho-train-length (ETL)), trigger pulse, and effective TR (which dependson the trigger pulse). MRI system 100 can perform dark-blood TSEsequences according to parameter values selected based on the desiredimaging results and characteristics. For example, different TSE MRIsequences can be configured for T1 or T2 image contrast (T1- orT2-weighting, respectively), depending on the selected parameters, as isknown in the art.

Conventionally, a trigger pulse of one means that the paired sequenceincluding both DB-prep and data readout is repeated every heartbeat. Inother words, every heartbeat is a “use heartbeat” in which DB-prep anddata readout occurs. A trigger pulse of two means that this sequence isexecuted every other heartbeat and the intermediate heartbeats are notused for imaging but for magnetization recovery. In this case “useheartbeats” and “recovery heartbeats” occur in an alternating manner.For a trigger pulse of three, two recovery heartbeats follow one useheartbeat.

The effective TR parameter, which is directly related to the quality ofthe contrast in the acquired image, is the amount of time betweenDB-prep being repeated. Since the paired sequence which includes DB-prepis timed to a particular point in the cardiac cycle, the effective TRparameter equals an integer multiple of the RR-interval (in seconds).The effective TR is thereby based on the trigger pulse. In particular,effective TR equals the RR-interval (in seconds) multiplied by thetrigger pulse (e.g., trigger pulse of one means that effective TR equalsone RR interval, trigger pulse of two means that effective TR equals twoRR intervals, etc.).

In T2-weighting, an imaging sequence is run with a relatively longereffective TR (e.g., at least 1800 ms), which may require, for example, atrigger pulse of two (for an average RR-interval of approximately 900ms). Higher heart rates with shorter RR-intervals may require a triggerpulse of three to ensure a sufficiently long effective TR. Therelatively long effective TR minimizes the effect of T1 weighting. Along TE between 60 ms and 80 ms may be used to maximize T2 weighting.Together, the long TE and long effective TR result in as pureT2-weighting as possible in the confinement of a breath-hold.

For T1-weighting, the TSE sequence may be run with a trigger pulse ofone in order to use the shortest possible effective TR (one RR-interval)to provide maximum T1 weighting. As described herein, a higher triggerpulse reduces the T1-weighting and therefore is not practical for aT1-weighted TSE sequence. A short TE in the range, for example, of 3-15ms may be selected to impart T1-contrast. Also, the number of acquiredechoes in the echo-train may be set to be relatively low (about 10-15echoes, in one embodiment) to limit the ETL, as too long of an echotrain would cause unwanted T2-weighting.

FIG. 2 is a diagram illustrating some features of a typical TSE MRIsequence, specifically its dark blood preparation. In an exemplaryembodiment, a heart 200 is targeted for imaging. An example ECG wave 210represents the cardiac cycle of the heart 200. The ECG wave 210 has asignal peak 220 known as the R-wave, indicating that the heart enters anew cardiac cycle. Cardiac contraction generally begins 50 ms-100 msafter the R-wave. The heart contracts and ejects blood (systole) beforerelaxing and refilling (diastole) and then restarting the cardiac cycleat the next R-wave.

The DB-prep module 110 is configured to apply magnetization pulses to animaging volume 230. In an exemplary embodiment, the DB-prep occursthrough double-inversion in which two 180° magnetization pulses areapplied. The first 180° pulse is nonselective, inverting themagnetization for all slices within the imaging volume 230. The second180° pulse, which immediately follows the first 180° pulse, is sliceselective, returning the magnetization of only those features in aselected slab 240 back to the opposite direction. In this way, themyocardium and other stationary tissues within slab 240 have theirsignals preserved and slab 240 is called a “preservation slab;” but theblood outside slab 240 has an inverted magnetization. From the time ofthe application of the dark-blood preparation until the data readout inlate diastole this blood from outside slab 240 flows into slab 240 whilesimultaneously undergoing magnetic recovery with time constant T1. Thedata capture module 120 performs a readout of an imaging slice 250within the imaging slab 240 to capture data associated with the heartduring the associated heartbeat.

The data readout performed by the data capture module 120 also has aneffect on the tissue being imaged. In particular, the data readout stepaffects the T1-weighting of the heart tissue in imaging slice 250. Ifthe data readout step is not performed during every heartbeat, themagnetization tends toward T2-weighting and maximum T1-weighting is notachieved. As a result, T1-weighted TSE is always run with a triggerpulse of one. While the described embodiment is for TSE sequences usingturbo-spin echo trains for data readout, other embodiments may beapplicable to other types of readouts. Examples of other data readoutsthat can be used for T1-weighted imaging include gradient-echo readoutsand steady-state free precession readouts.

After DB-prep, the inverted magnetization of the inflowing bloodrecovers to the point of zero magnetization (before returning tonon-inverted magnetization). Blood with zero or approximately zeromagnetization is known as nulled blood or dark blood, as a data captureof the non-magnetized blood will produce a dark or black area in an MRimage. The point of zero magnetization is referred to herein as the“dark-blood point.”

Data readout should be timed to capture data at the dark blood point tooptimize dark-blood performance. In order for this to occur, the datareadout may be delayed until a systolic contraction to replacenon-inverted blood in the preservation slab 240 with inverted blood fromoutside of the preservation slab 240. This requires the readout to takeplace during diastole, which may be about 600 ms to 850 ms after theDB-prep at the R-wave. This timing is also advantageous in that themotion-sensitive TSE readout falls into a diastolic phase which bydefinition possesses little motion.

FIG. 3 illustrates an example of a T1-weighted TSE pulse 300 sequence inwhich the subject has a relatively low heart rate (long RR-interval).The top line represents an ECG wave 310 for triggering each step ofDB-prep 320 a, 320 b. Each DB-prep 320 a, 320 b immediately follows eachR-wave of the ECG wave 310. A corresponding step of data readout 330 a,330 b occurs after each DB-prep 320 a, 320 b, respectively, and istriggered based on a selected timing after the associated DB-prep 320a-b.

Each data readout 330 a, 330 b is preferably timed to occur at the darkblood point of the inflowing blood at diastole. The magnetizationevolution of this inflowing blood is seen in the bottom diagram of FIG.3. The magnetization of the blood is inverted by DB-prep 320 a, 320 b(but not re-inverted because it is not in the preservation slab 240 atthe time of DB-prep 320 a, 320 b). The blood undergoes a recurringmagnetization recovery after every inversion by the DB-prep 330 a, 330 band is periodic with the RR-interval. The magnetization of tissue withinthe imaging slab is not shown but has maximum T1-weighting at the timeof readout.

When a subject's heart rate is low (e.g., less than 80 beats per minute(bpm)), high-quality dark blood performance is expected, as each datareadout 330 a-b successively occurs at the dark blood point. Theresulting images produced through TSE MRI can thus be expected toinclude clear demarcations between blood and tissue and should be ableto be relied upon for diagnosis. However, while this effective timingcan be achieved at low heart rates, higher heart rates do not allow forthe same results.

FIG. 4 illustrates an example of a T1-weighted TSE pulse sequence 400 inwhich the subject has a relatively high heart rate (short RR-interval).For example, 100 bpm (RR-interval of about 600 ms) is considered hereinto be a “high” heartrate. The top line represents an ECG wave 410 fortriggering each step of DB-prep 420 a, 420 b, 420 c, 420 d. As describedherein, each DB-prep 420 a, 420 b, 420 c, 420 d immediately follows eachR-wave of the ECG wave 410. Due to the high heart rate, the timing ofcorresponding data readouts 430 a, 430 b, 430 c, 430 d must beconsidered.

With a trigger pulse of one as mandatory for T1-weighting, the bloodoutside the preservation slab 240 sees so many inversion pulses per timeperiod that it is significantly magnetically saturated. As a result, themagnetization of inflowing blood oscillates within a significantlysmaller range compared to the lower heartrate case of FIG. 3. It followsthat the inflowing blood recovers to zero magnetization (reaches thedark blood point) very early after the R-wave, for example at 300 ms.However, the data readout cannot occur at this point because the heartis still in systole. The systolic phase has so much cardiac motion thata TSE readout usually yields undiagnostic images. Further, the heart isin a different location during systole than at the R-wave (where itstill has its diastolic position and shape), resulting in thepreservation slab 240 and imaging slice 250 being misaligned, leading toa non-diagnostic image. For example, there may be partial regionalinversion of the imaged slice, causing the data capture to misrepresentthe underlying features.

As shown in FIG. 4, the data readouts 430 a, 430 b, 430 c, 430 d can bemoved to the time period in which the heart is diastole. This generallyovercomes the heart movement/slab misalignment problem, but at this timeblood magnetization has partially recovered and has passed the darkblood point. This problem repeats at each data readout 430 a, 430 b, 430c, 430 d. As a result, the captured data does not include blood at thedark blood point and instead includes non-zero blood magnetization.Non-zero blood magnetization causes severe artifacts when readout withTSE due to its flow sensitivity which causes incorrect spatial encoding.Blood appears “smeared” across such TSE images, which are frequentlynon-diagnostic and thus not reliable.

FIGS. 5A and 5B show examples of two conventional dark-blood T1-weightedTSE images acquired in one subject at two slice locations. The subjectof these images had a relatively high heart rate at the time of imaging(e.g., greater than 80 bpm). It can be clearly seen that the blood isnot properly nulled, i.e., it is not completely black. Furthermore,there is a “haze” which overlays the heart, covering parts of themyocardium and thus reducing reliability of the image.

Therefore, because T1-weighted TSE requires a trigger pulse of one and ahigher heart rates involve heartbeats which occur too quickly for thedark blood point to match up with the heart being in diastole duringeach heartbeat, a conventional dark-blood T1-weighted TSE sequence doesnot produce high quality, reliable images in high heart rate subjects.Moreover, image quality worsens with decreasing RR.

Presently disclosed embodiments of MRI system 100 are configured toperform a TSE sequence which includes a data readout (or a dummy-readoutof the same magnetic saturation effect without using the readout data)during each heartbeat so that the tissue T1-weighting does not changefrom the conventional sequence, while executing the DB-prep only duringcertain heartbeats according to a trigger pulse determined by thesubject's RR-interval. Conventionally, a trigger pulse of one in TSE MRIresults in both DB-prep and data readout being performed everyheartbeat. However, only the data readout step keeps the tissuemagnetization in the imaged slice 250 in a steady state of maximumT1-weighting; the step of DB-prep does not create T1-weighting in theimaged slice 250. At least some disclosed embodiments thus “unpair” theDB-prep and data readout steps to allow DB-prep to be performed lessoften at high heart rates to avoid significant magnetic saturation ofblood, while maintaining the maximum T1-weighting provided by theperformance of the data readout with every heartbeat.

In order to provide the image reconstruction module 130 with the properdata for reconstructing an image, the data readouts which are performedduring heartbeats that do not also include DB-prep are considered“dummy” readouts, as these readouts do not include usable data (due tothe lack of a paired step of DB-prep). In other words, disclosedembodiments use only the readouts which are obtained during theheartbeats with a paired DB-prep for data acquisition. The purpose ofthe “dummy” readouts is to keep tissue magnetization in the maximumT1-weighted state. The “dummy” readouts are not used for imagereconstruction. In some embodiments, any data collected is discarded orignored. In other embodiments, no data is collected during these steps.In alternative embodiments, the “dummy” readout step is replaced with asimilar step which achieves the goal of maintaining T1-weighting. Forexample, the MRI system 100 may be configured to perform slice-selectivesaturation preparation steps which have the same T1-weighting effect asa the dummy readout step, also without the capture of data. These stepswhich replace a conventional data readout step during certain heartbeatsare generally referred to herein as steady-state maintenance steps.

FIG. 6 is a flowchart of an exemplary process 600 for producingT1-Weighted TSE MR images, according to a disclosed embodiment. In oneembodiment, MRI system 100 is configured to perform one or more steps ofthe process 600. The MRI system 100 may include computing elements, suchas a processor, memory, and I/O devices that are configured to carry outMRI functions. The process 600 is performed in relation to a subject andis arranged to capture data and produce MR images of the subject'sheart.

In step 610, the MRI system 100 measures the subject's heartrate. TheMRI system may include a heartrate monitoring component or may beconnected to one. Generally, the MRI system 100 is executed during abreath-hold. The MRI system 100 may use an average heartrate during thistime or may use a heartrate measurement prior to the breath-hold. TheMRI system 100 may be configured to obtain a heartrate in bpm or ameasured RR-interval, or determine an RR-interval based on a measuredbpm.

In step 620, the MRI system 100 identifies a DB-Prep trigger pulse formaximizing dark blood performance. The DB-prep trigger pulse is aparameter which identifies how often the DB-prep step will be performedduring the imaging sequence. In particular, the MRI system 100determines a value N as the DB-prep trigger pulse which indicates that aDB-prep step will be performed only every Nth heartbeat. A DB-preptrigger pulse of two means that DB-prep is performed every otherheartbeat, DB-prep trigger pulse of three means that DB-prep isperformed every third heartbeat, and so on.

The MRI system 100 determines the value N for the DB-prep trigger pulsebased on a parameter representative of the subject's heartrate, such asa value for the subjects heartrate (in BMP) or the RR-interval. Asdescribed herein, higher heartrates are not compatible with aconventional trigger pulse (DB-prep and data readout) of one becauseDB-prep occurs too often and magnetically saturates the blood in theimaging area, causing blood nulling to occur too early in each cardiaccycle. The MRI system 100 is configured to determine a more appropriatetrigger pulse which does not cause saturation and sufficiently delaysthe occurrence of the dark-blood point of the blood outside of theimaging slab such that the dark-blood point aligns with the heart beingin diastole (instead of occurring sooner during systole). The MRI system100 is configured to calculate the DB-prep trigger pulse as function ofthe parameter representative of the subject's heartrate (e.g., bpm orRR-interval). In one example, the DB-prep module 110 compares theparameter representative of the subject's heartrate to one or morethreshold values or uses a lookup tab to determine the DB-prep triggerpulse that best results in a data readout coinciding with the subject'sheart being in diastole and is as close to one as possible.

In step 630, the MRI system 100 performs a T1-weighted TSE imagingsequence according to the identified DB-prep trigger pulse. In disclosedembodiments, the TSE imaging sequence uses the identified DB-preptrigger pulse (N) in that the DB-prep module 110 is triggered only inevery Nth beat. As an example, a DB-prep trigger pulse of two means thatevery “use beat” (in which DB-prep is performed) is separated by aheartbeat in which no DB-prep is performed, referred to herein as a“blood recovery beat.” The DB-prep module 110 is preferably triggered bya physiological signal, such as an ECG or pulse ox wave. For example,the DB-prep module 110 may be triggered every Nth R-wave.

The TSE imaging sequence also includes data readouts performed by thedata capture module 120. In an exemplary embodiment, the data capturemodule 120 performs a data readout in every use beat. That is, for everyheartbeat which includes DB-prep, a data readout is performed duringthat heartbeat. The data readout is timed to occur during diastole whichis determined by the TSE imaging system 100 based on the heartrate(e.g., RR-interval).

In disclosed embodiments, the TSE imaging sequence further includessteady-state maintenance steps which occur during blood recovery beats.The steady-state maintenance step may be a magnetic saturation pulse andtake the place of the data readout step during blood recovery beats. Thesteady-state maintenance step maintains the magnetic saturation of thetissue within the imaging slice 250 in the same or similar manner as adata readout step. In an exemplary embodiment, the steady-statemaintenance step is a “dummy” readout in which the data capture module120 performs a data readout, but data is not ultimately used in imagereconstruction.

In step 640, the MRI system 100 discards or ignores the “dummy” readout.In one example, the data capture module 120 deletes or overwrites thedata associated with “dummy” readouts and does not transmit anything tothe image reconstruction module 130. In other embodiments, the datacapture module 120 delivers data associated with “dummy” readouts to theimage reconstruction module 130. The image reconstruction module 130determines that the data is associated with a “dummy” readout anddiscards, ignores, or otherwise deletes the data. For example, the imagereconstruction module 130 may use the DB-trigger pulse to determinewhich received data sets are associated with use beats and which datasets are associated with blood recovery beats. The image reconstructionmodule 130 may subsequently utilize the data sets associated with usebeats and discard, ignore, or otherwise delete data sets associated withblood recovery beats.

In step 650, the MRI system 100 reconstructs an MR image using thereceived data. The image reconstruction module 130 uses data captured bythe data capture module 120 to produce an MR image. The MR image ispreferably in the same form and format as a conventional MR image,including image slices of the subject's heart. As described herein, theimage reconstruction module 130 uses only data sets which are capturedduring use beats and either discards or never receives data setsassociated with blood recovery beats. The resulting MR image isT1-weighted due to the one of the combination of data readouts andsteady-state maintenance steps occurring during each heartbeat duringthe sequence.

FIG. 7 shows a T1-weighted TSE sequence 700 with DB-prep trigger pulseof two, according to an exemplary embodiment. The top line represents anECG wave 710 for triggering each step of DB-prep 720 a, 720 b. The TSEsequence further includes data readout steps 730 a, 730 b andsteady-state maintenance steps 740 a, 740 b. The blood flowing into theimaging slab magnetically recovers over the course of two heartbeats.This is due in part to the spacing of the steps of DB-prep 720 a, 720 b,which inhibits magnetic saturation of the blood which would causemagnetic recovery to occur too early in the cardiac cycle. As a result,the dark blood point occurs later and overlaps with a time period inwhich the subject's heart is in diastole, providing consistency to theimage slices and reducing the chance of artifacts and blurring or hazingof the image. Moreover, the subject's heart tissue in the imaging slabreceives a data readout 730 a, 730 b or a steady-state maintenance step740 a, 740 b at every heartbeat, thereby mimicking a conventionaltrigger pulse of one and maximizing T1-weighting of the image.

In the embodiment of FIG. 7, the steady-state maintenance steps 740 a,740 b are “dummy” readouts in which the data capture module 120 performsa data readout similar to the data readouts 730 a, 730 b. The “dummy”readouts include a data capture, however the data is not used for imagereconstruction.

FIG. 8 shows another embodiment of an exemplary TSE MRI sequence 800with respect to an ECG wave 810. The sequence 800 is similar to thesequence 700, including DB-prep 820 a, 820 b according to a DB-preptrigger pulse of two, data readouts 830 a, 830 b during use beats andsteady-state maintenance steps 840 a, 840 b during blood recovery beats.However, in sequence 800, the steady-state maintenance steps 840 a, 840b are slice-selective saturation preparation pulses instead of “dummy”readouts. The data capture module 120 (or another component of MRIsystem 100, such as DB-prep module 110 or another prep module not shown)is configured to apply a magnetic pulse which mimics that of the datareadouts 830 a, 830 b in that it produces a slice-selective pulse whichsaturates transverse and longitudinal magnetization of the tissue. Theslice-selective saturation preparation has substantially the same effectas a data readout, because a readout of typical length (50 ms to 150 ms)also saturates transverse and longitudinal magnetization in the imagingslab. The slice-selective saturation preparation has the same magneticsaturation effect as a data readout, but does not capture any data,which advantageously requires lower energy and power.

FIG. 9 shows yet another embodiment of an exemplary TSE MRI sequence 900with respect to an ECG wave 910. The sequence 900 is similar to thesequences 700 and 800, including DB-prep 920 a, 920 b, 920 c accordingto a DB-prep trigger pulse of two and data readouts 930 a, 930 b duringuse beats, and steady-state maintenance steps 940 a, 940 b, 940 c. Insequence 900, however, the steady-state maintenance steps 940 a, 940 b,940 c are slice—selective saturations and are integrated into theDB-prep 920 a, 920 b, 920 c. For example, the slice-selective saturationpreparation described with respect to FIG. 8 may be combined with thesteps of DB-prep 920 a, 920 b, 920 c. In this modified DB-prep (SR-DBprep), the slice-selective inversion preparation commonly used instandard DB-prep is replaced by a slice-selective saturation recovery(SR) preparation. In one embodiment, the slice-selective inversion pulseof each step of DB-prep is replaced by a slice-selective saturationpulse. In one embodiment, a spoiler gradient pulse is performed as partof the SR-DB prep, in addition to the non-selective inversion pulse andslice-selective saturation pulse. The spoiler gradient pulse may beperformed after the two other pulses of DB-Prep.

The integrated combination is in part possible because the steady-statemaintenance steps of the disclosed embodiments occur close enough intime to the steps of DB-prep such that moving the timing of thesaturation preparation to occur with the DB-prep of the next heartbeatdoes not significantly impact image contrast. This embodiment has theadvantage that the tissue magnetization during data readouts 930 a, 930b are independent of the duration of the previous RR-interval, as themagnetization in the prepared slab is reset with the saturation in theSR-DB-prep and is read out at exactly the same time after eachSR-DB-prep 920 a, 920 b, 920 c. Signal oscillations due to the naturalvariation of the RR-interval during the acquisition of one image andconcomitant ghosting artifacts are thus avoided.

The disclosed embodiments include TSE MRI sequences which are designedto maintain maximum T1-weighting by including data readouts or a similarsteady-state maintenance step with every heartbeat while also timing thedata readouts which are used in image reconstruction to instances inwhich the dark blood point occurs during diastole. The MRI system 100 isconfigured to perform a T1-weighted TSE sequence according to disclosedembodiments in order to produce an MR image with high quality dark bloodperformance. The disclosed sequences are particularly applicable toinstances in which the subject has a high heart rate (e.g., greater than80 bpm), but could be applied in other situations depending on thedesired characteristics of the MRI.

FIGS. 10A and 10B show T1-weighted TSE images acquired by a MRI systemusing a sequence consistent with those described herein, such as thoseshown in FIGS. 7-9. The images were acquired in the same subject at thesame two slice locations as those in FIGS. 5A-5B. The MRI system 100used parameters which follow a conventional T1-weighted TSE sequenceexcept for that a DB-trigger pulse of greater than one was used and“dummy” readouts were used during blood recovery beats. A comparison tothe images of FIGS. 5A-5B shows a clear improvement of dark bloodperformance and depiction of the myocardium.

FIG. 11 illustrates an exemplary computing environment 1100 within whichembodiments of the invention may be implemented. For example, thiscomputing environment 1100 may be configured to execute an imagingprocess performed by the MRI system 100. The computing environment 1100may include computer system 1110, which is one example of a computingsystem upon which embodiments of the invention may be implemented.Computers and computing environments, such as computer system 1110 andcomputing environment 1100, are known to those of skill in the art andthus are described briefly here.

As shown in FIG. 11, the computer system 1110 may include acommunication mechanism such as a bus 1105 or other communicationmechanism for communicating information within the computer system 1110.The computer system 1110 further includes one or more processors 1120coupled with the bus 1105 for processing the information. The processors1120 may include one or more central processing units (CPUs), graphicalprocessing units (GPUs), or any other processor known in the art.

The computer system 1110 also includes a system memory 1130 coupled tothe bus 1105 for storing information and instructions to be executed byprocessors 1120. The system memory 1130 may include computer readablestorage media in the form of volatile and/or nonvolatile memory, such asread only memory (ROM) 1131 and/or random access memory (RAM) 1132. Thesystem memory RANI 1132 may include other dynamic storage device(s)(e.g., dynamic RAM, static RAM, and synchronous DRAM). The system memoryROM 1131 may include other static storage device(s) (e.g., programmableROM, erasable PROM, and electrically erasable PROM). In addition, thesystem memory 1130 may be used for storing temporary variables or otherintermediate information during the execution of instructions by theprocessors 1120. A basic input/output system (BIOS) 1133 containing thebasic routines that help to transfer information between elements withincomputer system 1110, such as during start-up, may be stored in ROM1131. RAM 1132 may contain data and/or program modules that areimmediately accessible to and/or presently being operated on by theprocessors 1120. System memory 1130 may additionally include, forexample, operating system 1134, application programs 1135, other programmodules 1136 and program data 1137.

The computer system 1110 also includes a disk controller 1140 coupled tothe bus 1105 to control one or more storage devices for storinginformation and instructions, such as a hard disk 1141 and a removablemedia drive 1142 (e.g., floppy disk drive, compact disc drive, tapedrive, and/or solid state drive). The storage devices may be added tothe computer system 1110 using an appropriate device interface (e.g., asmall computer system interface (SCSI), integrated device electronics(IDE), Universal Serial Bus (USB), or FireWire).

The computer system 1110 may also include a display controller 1165coupled to the bus 1105 to control a display 1166, such as a cathode raytube (CRT) or liquid crystal display (LCD), for displaying informationto a computer user. The computer system 1110 includes an input interface1160 and one or more input devices, such as a keyboard 1162 and apointing device 1161, for interacting with a computer user and providinginformation to the processor 1120. The pointing device 1161, forexample, may be a mouse, a trackball, or a pointing stick forcommunicating direction information and command selections to theprocessor 1120 and for controlling cursor movement on the display 1166.The display 1166 may provide a touch screen interface which allows inputto supplement or replace the communication of direction information andcommand selections by the pointing device 1161.

The computer system 1110 may perform a portion or all of the processingsteps of embodiments of the invention in response to the processors 1120executing one or more sequences of one or more instructions contained ina memory, such as the system memory 1130. Such instructions may be readinto the system memory 1130 from another computer readable medium, suchas a hard disk 1141 or a removable media drive 1142. The hard disk 1141may contain one or more datastores and data files used by embodiments ofthe present invention. Datastore contents and data files may beencrypted to improve security. The processors 1120 may also be employedin a multi-processing arrangement to execute the one or more sequencesof instructions contained in system memory 1130. In alternativeembodiments, hard-wired circuitry may be used in place of or incombination with software instructions. Thus, embodiments are notlimited to any specific combination of hardware circuitry and software.

As stated above, the computer system 1110 may include at least onecomputer readable medium or memory for holding instructions programmedaccording to embodiments of the invention and for containing datastructures, tables, records, or other data described herein. The term“computer readable medium” as used herein refers to any medium thatparticipates in providing instructions to the processor 1120 forexecution. A computer readable medium may take many forms including, butnot limited to, non-volatile media, volatile media, and transmissionmedia. Non-limiting examples of non-volatile media include opticaldisks, solid state drives, magnetic disks, and magneto-optical disks,such as hard disk 1141 or removable media drive 1142. Non-limitingexamples of volatile media include dynamic memory, such as system memory1130. Non-limiting examples of transmission media include coaxialcables, copper wire, and fiber optics, including the wires that make upthe bus 1105. Transmission media may also take the form of acoustic orlight waves, such as those generated during radio wave and infrared datacommunications.

The computing environment 1100 may further include the computer system1110 operating in a networked environment using logical connections toone or more remote computers, such as remote computer 1180. Remotecomputer 1180 may be a personal computer (laptop or desktop), a mobiledevice, a server, a router, a network PC, a peer device or other commonnetwork node, and typically includes many or all of the elementsdescribed above relative to computer system 1110. When used in anetworking environment, computer system 1110 may include modem 1172 forestablishing communications over a network 1171, such as the Internet.Modem 1172 may be connected to bus 1105 via user network interface 1170,or via another appropriate mechanism.

Network 1171 may be any network or system generally known in the art,including the Internet, an intranet, a local area network (LAN), a widearea network (WAN), a metropolitan area network (MAN), a directconnection or series of connections, a cellular telephone network, orany other network or medium capable of facilitating communicationbetween computer system 1110 and other computers (e.g., remote computer1180). The network 1171 may be wired, wireless or a combination thereof.Wired connections may be implemented using Ethernet, Universal SerialBus (USB), RJ-11 or any other wired connection generally known in theart. Wireless connections may be implemented using Wi-Fi, WiMAX, andBluetooth, infrared, cellular networks, satellite or any other wirelessconnection methodology generally known in the art. Additionally, severalnetworks may work alone or in communication with each other tofacilitate communication in the network 1171.

The embodiments of the present disclosure may be implemented with anycombination of hardware and software. In addition, the embodiments ofthe present disclosure may be included in an article of manufacture(e.g., one or more computer program products) having, for example,computer-readable, non-transitory media. The media has embodied therein,for instance, computer readable program code for providing andfacilitating the mechanisms of the embodiments of the presentdisclosure. The article of manufacture can be included as part of acomputer system or sold separately.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

An executable application, as used herein, comprises code or machinereadable instructions for conditioning the processor to implementpredetermined functions, such as those of an operating system, a contextdata acquisition system or other information processing system, forexample, in response to user command or input. An executable procedureis a segment of code or machine readable instruction, sub-routine, orother distinct section of code or portion of an executable applicationfor performing one or more particular processes. These processes mayinclude receiving input data and/or parameters, performing operations onreceived input data and/or performing functions in response to receivedinput parameters, and providing resulting output data and/or parameters.

A graphical user interface (GUI), as used herein, comprises one or moredisplay images, generated by a display processor and enabling userinteraction with a processor or other device and associated dataacquisition and processing functions. The GUI also includes anexecutable procedure or executable application. The executable procedureor executable application conditions the display processor to generatesignals representing the GUI display images. These signals are suppliedto a display device which displays the image for viewing by the user.The processor, under control of an executable procedure or executableapplication, manipulates the GUI display images in response to signalsreceived from the input devices. In this way, the user may interact withthe display image using the input devices, enabling user interactionwith the processor or other device.

The functions and process steps herein may be performed automatically orwholly or partially in response to user command. An activity (includinga step) performed automatically is performed in response to one or moreexecutable instructions or device operation without user directinitiation of the activity.

The system and processes of the figures are not exclusive. Othersystems, processes and menus may be derived in accordance with theprinciples of the invention to accomplish the same objectives. Althoughthis invention has been described with reference to particularembodiments, it is to be understood that the embodiments and variationsshown and described herein are for illustration purposes only.Modifications to the current design may be implemented by those skilledin the art, without departing from the scope of the invention. Asdescribed herein, the various systems, subsystems, agents, managers andprocesses can be implemented using hardware components, softwarecomponents, and/or combinations thereof. No claim element herein is tobe construed under the provisions of 35 U.S.C. 112(f) unless the elementis expressly recited using the phrase “means for.”

1. A computer-implemented method for performing a cardiovascularT1-weighted turbo-spin-echo magnetic resonance imaging sequence,comprising: receiving a physiological signal from a subject, thephysiological signal representative of the subject's heartbeat;performing dark-blood preparation according to a trigger pulse of N,wherein the dark-blood preparation occurs only in every Nth heartbeatand N is greater than 1; performing a data readout in every Nthheartbeat, wherein the data readout includes capturing imaging dataassociated with an imaging slice; performing a steady-state maintenancestep, wherein the steady-state maintenance steps are performed only forevery heartbeat which does not include a data readout; reconstructing aT1-weighted image of the imaging slice based on the imaging datareceived as a result of the data readouts.
 2. The computer-implementedmethod of claim 1, wherein the physiological signal is anelectrocardiogram wave.
 3. The computer-implemented method of claim 2,wherein the dark-blood preparation is triggered by at the R-wavepreceding every Nth heartbeat.
 4. The computer-implemented method ofclaim 1, wherein the physiological signal is a pulse oximetry wave. 5.The computer-implemented method of claim 1, wherein the steady-statemaintenance step is a “dummy” readout in which imaging data iscollected.
 6. The computer-implemented method of claim 5, wherein theimage is reconstructed from a data set which does not include theimaging data associated with the “dummy” readouts.
 7. Thecomputer-implemented method of claim 1, wherein the steady-statemaintenance step is a slice selective saturation pulse which saturatestransverse and longitudinal magnetization of the tissue and does notinclude a data readout.
 8. The computer-implemented method of claim 1,wherein the steady-state maintenance step is integrated with thedark-blood preparation for a combined dark-blood and saturationpreparation step.
 9. The computer-implemented method of claim 8, whereinthe combined dark-blood and saturation preparation step comprises aslice selective saturation pulse which saturates transverse andlongitudinal magnetization of the tissue.
 10. A computer-implementedmethod for producing a cardiovascular T1-weighted magnetic resonanceimage, comprising: receiving a parameter representative of a subject'sheartrate; determining a trigger pulse value N for an MRI sequence basedon the parameter representative of the subject's heartrate; performingthe MRI sequence, including: performing dark-blood preparation accordingto a trigger pulse of N, wherein the dark-blood preparation occurs onlyin every Nth heartbeat; and performing one of a data readout or asteady-state maintenance step for every heartbeat, wherein the datareadout includes capturing imaging data associated with an imaging sliceand both the data readout and the steady-state maintenance step saturatetransverse and longitudinal magnetization of the tissue; andreconstructing a T1-weighted image of the imaging slice based on theimaging data received as a result of the data readouts.
 11. Thecomputer-implemented method of claim 10, wherein the parameterrepresentative of the subject's heartrate is a physiological signal. 12.The computer-implemented method of claim 10, wherein the parameterrepresentative of the subject's heartrate is an average value for theheartrate.
 13. The computer-implemented method of claim 10, whereindetermining the trigger pulse value N includes comparing the parameterrepresentative of the subject's heartrate to one or more thresholdvalues or using a lookup table.
 14. The computer-implemented method ofclaim 10, wherein the data readout and the maintenance pulse occur whilethe subject's heart is in diastole.
 15. The computer-implemented methodof claim 10, wherein the maintenance steady-state step includes a datareadout that produces a data set which is not used in the imagereconstruction.
 16. The computer-implemented method of claim 10, whereinthe steady-state maintenance step is integrated with the dark-bloodpreparation performed during a subsequent heartbeat.
 17. A T1-weightedturbo-spin-echo magnetic resonance imaging system configured to capturedata associated with a subject's heart during a time period and produceMR images, comprising: a dark-blood preparation module configured toperform dark-blood preparation through double inversion during some, butnot all of the heartbeats within the time period; a data capture moduleconfigured to perform data readouts to capture imaging data of animaging slice during every heartbeat within the time period; and animage reconstruction module configured to reconstruct a T1-weightedimage based on the imaging data, wherein the image reconstruction modulediscards or ignores imaging data received from the data capture modulewhich was captured during heartbeats in which the dark-blood preparationmodule did not perform dark-blood preparation.
 18. The system of claim17, wherein the dark-blood preparation module determines a trigger pulseN and performs dark-blood preparation only for every Nth heartbeat. 19.The system of claim 18, wherein N is greater than one.
 20. The system ofclaim 18, wherein the dark-blood preparation module determines thetrigger pulse N based on a parameter representative of the subject'sheartrate.